Ear cups are normally used in hearing protector units. Two ear cups may be connected via a connection unit to a head band to form a hearing protector unit, or be connected via a connection unit to a helmet to form a helmet including a hearing protector unit. For the hearing protector unit to function properly, the ear cups should be placed at a certain location over the user's ears. Due to different head shapes of different users, the ear cups need to be adjustable in height relative to the head band or helmet. Even a small misplacement of the ear cup over the user's ear may provide a significant loss in the sound-attenuating function of the hearing protector unit.
A known way of solving the problem of height adjustment to ear cups in hearing protector units is to provide the connection unit as a height adjustment arrangement comprising a steel wire that is connected to an ear cup via a plastic and/or rubber holder. The holder is designed to provide a friction force between the steel wire and the holder. A user may pull or push the ear cup to a desired height with a force larger than the friction force. When the ear cup is pulled or pushed to the desired height, the friction force between the parts in the height adjustment arrangement will hold the ear cup at that height during use of the hearing protector unit.
A problem with such height adjustment arrangement for an ear cup in a hearing protector unit is that the parts in the height adjustment arrangement, i.e. the holder and the steel wire, may be worn out over time such that the friction force will be reduced. When the friction force becomes reduced, the ear cups in the hearing protector unit will eventually drop to maximum extended position of the height adjustment arrangement, irrespectively which height of the ear cups the user tries to set. I.e. the friction force trying to hold the ear cup at a certain height becomes less than the force of gravity provided by the ear cup. Thereby, the ear cups are not correctly positioned at the user's ears, resulting in that the sound-attenuating function of the hearing protector unit will be significantly impaired. This problem may be extra significant for electronic hearing protector units which contain heavy batteries that may increase the force of gravity reverse of the friction force during use of the hearing protector unit. Further, such problem will make the hearing protector unit very uncomfortable for the user due to the unsatisfactory fit. The same problem may be caused by differences in production tolerances of the steel wire and the holder. A small difference in the thickness of steel wires for such height adjustment arrangements would cause different friction forces between a steel wire and a holder. Therefore, a very small tolerance in the steel wire diameter is needed to secure a correct friction force when arranged to the holder.
U.S. Pat. No. 1,329,658 discloses a telephone headband hearing unit with a connection unit that may be used in a hearing protector unit. The connection unit comprises a holder with a hollow interior for receiving a part from the head band. The connection unit further comprises a nut cap adapted to integrate with the holder. The holder and the nut cap each comprises a tapering part, in a truncated cone shape, provided with threads to integrate with each other. Such solution alleviates some of the problems above with friction dependency. However, the solution in U.S. Pat. No. 1,329,658 has a problem in that the connection between the holder and the nut cap may be insecure.
Consequently, there is a need for a height adjustment arrangement for the ear cups in a hearing protector unit that provides a reliable and secure solution over long time use.